Rotary kiln for extraction of mercury from its ores



I May 9, 1944. c, F. DEGNER 2,348,673

ROTARY KILN FOR EXTRACTION 0E MERCURY FROM ITS ORES I Filed Sept. 8, 1941 4 Sheets-Sheet 1 javera i'or C/zarZeS'ZZggrzez agy :W, Mm, flmgamm.

y 1944- C. F. DEGNER 2,348,673 ROTARY KILN FOR EXTRACTI9N OF MERCURY FROM ITS ORES FiledSept. 8. 1941 4 Sheets-Sheet 2 =k 4 #3.. 28g zVII/II/I/II/I/II/IIIIIII/1111111111101111/11/14 Weraiar CVearZes ii'fiqgzzeza @wwmam mda May 9, 1944. c. F. IOEGNER ROTARY KILN FOR EXTRACTION OF MERCURY FROM ITS ORES 4 Sheets-Sheet 3 Filed Sept. 8 1941 ba y'zm, 2w,

May 9, 1944. c. F. DEGNER 3 ROTARY KILN FOR EXTRACTION OFNIERCURY FROM ITS '0RES 'Filgd Sept. 8, 1941" 4 Sheets-Sheet 4 Patented May 9, 1944 UNITED STATES RATENT OFFICE ROTARY KILN FOR EXTRACTION OF MERCURY FROM ITS ORES 2 Claims.

This invention relates to a rotary kiln primarily adapted for the extraction of mercury from its ores.

As is well known, the recovery of mercury from cinnabar which is the principal ore involves many difficulties. The mercury compounds are quite unstable and yield some mer cury with considerable ease. However, the mercury produced has a great tendency to pervade all of its surroundings and to escape either as a gas, mist or liquid. Furthermore the last portions of the mercury are extremely diflicult to separate from the ore.

In the beginning brick or masonry structures were used for the furnaces but it was soon found that the furnaces became saturated with liquid mercury. Later iron shields were used on the outside of the furnaces to prevent escape of mercury through the walls. Attempts to use iron in direct contact with the mercury ores and the mercury vapors have not been particularly'successful, not only because of the acid character of the vapors within the furnace, but because the iron tended to flake off and the flakes had a defluxing influence upon the flux used to facilitate the removal of mercury from the ores.

Th tendency of mercury to escape either as a gas or mist is also well known. Hitherto attempts have been made to lessen this tendency by maintaining a slightly subatmospheric pressure within the furnace by means of a fan. These eiforts have not been particularly successful and the amounts of air introduced had not been subject to control. The result has been that if the fan were operated too strongly, a great deal of mercury would be exhausted through the fan, whereas if it were operated less strongly, explosive mixtures might be produced within the furnace.

The present furnace overcomes all of these difficulties and at the same time provides a means of recovering mercury which utilizes a minimum of heat, will last indefinitely, and recovers a maximum of mercury from the ores.

Th device is illustrated in the drawings in which Fig. l i a side elevation of the furnace and its connections, partly in section; Fig. 2 is a fragmentary longitudinal section of the lefthand portion of the apparatus as viewed in Fig. 1; Fig. 3 is a fragmentary longitudinal section of the right-hand portion of the apparatus as viewed in Fig. 1; Fig. 4 is a transverse section taken on line 4 of Fig. 1, showing the hopper and gate arrangement; Fig. 5 is a transverse section taken on the line 5 of Fig. 1, showing discharge means on the peripheral shape of the drum; Fig. 6 is a transverse section taken on line 6 of Fig; showing the means of conveying residual matter through a liquid seal; and Fig. '7 is a transverse section along the line 1 in Fig. 1, showing the detail of the driving means for the screw conveyor for removing the ashes.

The apparatus consists of a hood ll covering the apparatus, a drum l0 which is rotatably mounted upon a hollow entrance bearing 35 and a hollow exhaust bearing 40. The charge is supplied to the kiln through a hopper 50. Residue is withdrawn through the fluid seal 50, and

vapors may be withdrawn through either bearing as will be hereinafter described.

The drum l0 consists of a steel shell 12 (preferably of stainless steel), which is provided with corrugations l3 of a substantial depth, and having sharp edges l4 and I5. A drum having an over-all length of approximately 8 ft. and a diameter of 30 in. and using lZ-gauge stainless steel, containing 25% chromium and 12% nickel, has proved quite satisfactory with corrugations approximately 3 in. in'depth and 6 in. across. These corrugations have been found extremely helpful in bringing each small portion of the charge into localized heat zones at intermittent periods. Heat is preferably supplied to the drums by external means such as the burners I5.

The burners may use either oil or gas or other heat, depending upon the most economical source. of supply. The drum is provided at the entrance end with a hollow co-axial extension H which serves as a journal for the bearing 30 and is provided at the exhaust end with a co-axial extension l8 which serves as a journal for the bearing 40. Between the extension I1 and the bearing 30 is packing H! which is enclosed by the packing gland or stuffing box 25. Between the extension I8 and the bearing 40 is packing 2|. A second annular packing gland 22 forms a stufling box about the bearing 40 and the extension l8. The extension I8 is supported in the frame 23 by the trunnions 24 and the extension I! is supported in the frame by trunnions 25.

The ore, which is usually cinnabar, is supplied through the hopper and the air lock 5| to the passageway 3| within the bearing 30. The air lock is of any suitable form and is shown in Figure 4:. As there indicated, an upper gate 52 and a lower gate 53 are provided with a chamber 54 between them. Gate 52 is operated by the arm 55, and gate 53 by the arm 56. These arms may be periodically actuated in any suitable mechanical manner or they may be hand operated. In

operation the gate 52 is opened while the gate 53 is closed, allowing a charge of ore to fill the chamber 54, after which gate 52 is closed and gate 53 may be opened whenever desired, thus supplying a charge of ore to the chamber 3! without opening that chamber to the air.

In the chamber 3| is a hollow shaft 32 coaxially mounted with the drum I and bearing a screw member 33 so adjusted as to convey ore from the outlet 51 of chamber 54 into the drum Ill. The end of the hollow shaft 32 adjacent the drum is supported in a spider 3 welded to the shaft at 35 and to the extension 11. Rotation of the drum thus serves to rotate the shaft 32 and the screw member 33. other end of the shaft is closed by a detachable cap 36. If desired, the cap may be removed and mercury vapors taken from this end of the drum.

The chamber 3| is closed at its outer end by the stuffing box 31, and trunnions 38 are provided as an additional support for the shaft.

The drum itself may be driven in any suitable fashion as by power applied to the gear member 29 on the extension l8.

In its passage through the drum If! the ore is held in the depressions of the troughs formed by the corrugations l3 and it is preferred that the rate of supply of ore to the drum shall be low enough merely to maintain a relatively shallow layer of ore. It is particularly desired not to have the ore extend substantially above the troughs. Preferably the troughs are maintained only partially full of mercury ore. During the rotation of the drum the ore is, therefore, continuously lifted in the troughs well up into the upper portions of the drum and then dropped, thus efficiently turning the ore and bringing all parts of it into contact with the heat. Furthermore the sharp angles of the troughs serve to bring increments of the ore successively into contact with localized heat conditions, thus serv ing to drive off the last traces of mercury. A temperature preferably below 800 F. is maintained within the drum, depending upon the type of ore used, the rapidity of through-put desired, and other conditions. It is preferred that the temperature be substantially uniform from one end of the drum to the other, and the burners are adjusted to secure this result. The rate of rotation of the drum depends on numerous factors. With a 30 in. drum a rate of to 2 revolutions per minute is preferred.

Near the outlet of the drum a series of fins 26 is provided. These fins pick up the ashes and drop them into the hollow bearing 40 which is provided with an opening 4| in its upper portion co-extensive with the fins. A hollow shaft 42 extends through the bearing 40 being secured in a spider 21 in the inner end of the bearing and a stuffing box 44 at the other end. A screw member 45 is secured to the outer side of the shaft and serves to carry the ashes through the chamber 46 within the bearing 49 to the passageway Bl of the water sealBU.

Vapors from the drum are removed through the passageway 41 in the hollow shaft 42 by means of a centrifugal fan 48 and are supplied to the radiation system 49 in any suitable form. This may consist merely of an iron pipe a few feet in length inclined downwardly. The mercury condenses within the pipe and the sulfur vapors pass off through it.

The shaft 42 is driven by the drum through The the arrangement shown in Figure '7. This comprises a spider 21 carrying a ring 28 provided with slots 28a. A pair of lugs 2812 are welded to the shaft 42 and fit into and lock in the slots 28a.

The ashes are fed by the conveyor 45 to the chamber 6| of the water seal 60. The ashes drop through 6| into a tube 62 in the water bath 63. The tube 62 contains a worm 64 feedin upwardly and the ashes are discharged from the opening 65 in the tube 62. The worm 64 is driven by the shaft 66 and may be driven through suitable gears 61 and G3 on the belt 69 from the same source of power as that used for the drum.

As will be seen from the foregoing discussion, the'entire drum is sealed against the admission of air. The drum itself, because of its exposure to heating and cooling, is made of stainless steel. The remainder of the apparatus may be made from ordinary steel or iron products.

Because of the lack of air it is possible to pro-- ceed with the recovery of mercury in a new manner. Processes hitherto have employed either air or lime to react with the sulfur generated by decomposition of cinnabar. The present process, because of its continuous nature and absence of air, is carried out on a different chemical basis. Because of the fact that a constant temperature is maintained up to the condenser, it is possible to prevent the mercury from recombining with the sulfur and to pass the latter off into the condenser or into the atmosphere while condensing merely the mercury.

While theoretically it has been heretofore supposed that mercruy and sulfur in the gaseous form immediately recombine upon cooling, excellent yields of mercury have been obtained by the use of this process. Furthermore the theoretical boiling point of sulfur is much above that of mercury; nevertheless, using an open pipe condenser 3 in. in diameter and 4 ft. long in connection with a drum of the size heretofore described, no substantial amounts of sulfur are condensed with the mercury. On the contrary, the mercury condenses in extremely pure metallic form and the yields obtained have exceeded those obtainable by other commercial methods.

The design apparatus here shown makes it possible to control the temperature accurately and rapidly within the drum, and this charac-,

teristic contributes in an important way to the success of the present process. Being thin walled, metallic, and there being only a short distance between the initial application of heat and the condensing zone, the material may be held at a uniform high temperature until just before sudden cooling.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom.

What I claim as new, and desire to secure by Letters Patent, is:

1. A rotary kiln comprising a sealed horizontal drum, a hollow bearing near each end of the drum, a hopper communicating through one of said hollow bearings'with one end of the drum, air lock means in "the hoppenmeans within the drum at the exit end thereof .for elevating ashes into the hollow bearing-liquid sealed means for removing ashes through the bearing, means for removing ashes from the drum, said hollow bearing including an open top extension within the drum, and means secured to the drum for elevating ashes and depositing them within the 5 open top hollow bearing.

CHARLES F. DEGNER. 

